Justin Bronk basically says that the J-50 and J-36 are technology demonstrators flown in open air for propaganda purposes, and that China is keeping two production lines for heavy fighters open out of communist ideology. Do you agree?
I think you're mischaracterizing what he said a bit. He said it's possible that they're both demonstrators flying in the open, but also possible that they're of two real parallel developments. He then immediately follows up with citations of multiple cases of other PLAAF parallel developments, while also noting that he doesn't speak mandarin and is not as well versed at PLA watching as
@Blitzo or
@Deino. To me, that portion sounds more like him bringing up the often repeated idea of the two 6th gens being TDs that very likely won't amount to anything real and then debunking it.
He does mention that China as a communist country is less averse to duplication of efforts, but also in addition to employment benefits it helps build out industrial base and provides China with more options, particularly noting that the J-36 and the J-50 are clearly very different aircrafts with different emphases. Notably, he mentions the J-36's size but does not use that as evidence of it being a strike-oriented aircraft, but simply as one which emphasizes high range/payload at high altitude/speed.
Overall I'd say not too bad of an analysis by someone who even himself admits is not an expert in the realm like the other better known western PLA watchers.